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United States Patent |
5,705,983
|
Tweadey, II
,   et al.
|
January 6, 1998
|
Glazing unit security system
Abstract
A glazing unit has a tempered glass pane or other frangible glazing pane
carrying a glazing pane breakage detector assembly. The detector assembly
includes spaced first and second electrically conductive bus pads formed
of electrically conductive material on a surface of the glazing pane. An
electrically resistive trace on the surface of the glazing pane is formed
of electrically resistive material different from the electrically
conductive material of the bus pads. The resistive trace establishes a
non-short electrical interconnection between the bus pads, which can be
formed of highly conductive material, such as silver-filled paint
currently in widespread commercial use. Such bus pads afford a
structurally sound attachment, with good electrical contact by soldering,
electrically conductive epoxy or the like upon which upstanding attachment
tabs are secured. Electrical leads can be attached to such upstanding tabs
to connect the detector assembly to suitable security circuitry. The
resistive trace is fragile, such that security circuitry can detect and
respond to loss of electrical connection between the bus pads upon
fracture of the glazing pane underlying the resistive trace. Security
circuitry also can detect a change in the resistance of the electrical
connection between the bus pads, such that security is not defeated by a
jumper cable between the bus pads. The resistance value of the resistive
trace between bus pads can be varied from one glazing pane to another to
further enhance security.
Inventors:
|
Tweadey, II; Robert F. (Farmington Hills, MI);
Gajewski; Kenneth J. (Woodhaven, MI)
|
Assignee:
|
Ford Motor Company (Dearborn, MI)
|
Appl. No.:
|
589669 |
Filed:
|
January 22, 1996 |
Current U.S. Class: |
340/550; 340/426.27; 340/426.28; 439/917 |
Intern'l Class: |
G08B 013/04 |
Field of Search: |
340/550,426
439/917
|
References Cited
U.S. Patent Documents
3609739 | Sep., 1971 | Walter | 340/550.
|
3863250 | Jan., 1975 | McCluskey, Jr. | 340/550.
|
4230918 | Oct., 1980 | Schroeder et al. | 340/550.
|
4796002 | Jan., 1989 | Heidman, Jr. | 340/426.
|
4804946 | Feb., 1989 | Elkowitz | 340/550.
|
4878044 | Oct., 1989 | Hickman | 340/550.
|
4999608 | Mar., 1991 | Galomb | 340/550.
|
5005020 | Apr., 1991 | Ogawa et al. | 343/713.
|
5114756 | May., 1992 | Mirabeau et al. | 427/379.
|
5139850 | Aug., 1992 | Clarke et al. | 428/192.
|
5198723 | Mar., 1993 | Parker | 313/634.
|
5389911 | Feb., 1995 | Madau | 340/426.
|
Primary Examiner: Swann; Glen
Attorney, Agent or Firm: Melotik, Esq.; Lorraine S.
Claims
We claim:
1. A glazing unit comprising a frangible glazing pane having a surface and
a glazing pane breakage detector assembly comprising:
first and second electrically conductive bus pads formed of electrically
conductive material on the surface of the glazing pane;
an electrically resistive trace on the surface of the glazing pane, formed
of electrically resistive material different from the electrically
conductive material of the bus pads, establishing a non-short circuit
electrical interconnection between the bus pads; and
first and second upstanding electrical lead attachment tabs secured in
electrical contact onto the first and second bus pads, respectively.
2. The glazing unit of claim 1 wherein the electrically resistive material
is polymeric material self-adhered to the surface of the glazing pane.
3. The glazing unit of claim 2 wherein the electrically resistive material
is selected from the group consisting of conductive epoxy and conductive
ink.
4. The glazing unit of claim 1 wherein the electrically resistive trace has
a non-straight line, irregular path between the bus pads.
5. A motor vehicle glazing unit security system comprising:
a glazing unit mounted in a motor vehicle and comprising a tempered glass
pane having a surface;
a glazing pane breakage detector assembling comprising:
first and second electrically conductive bus pads of electrically
conductive material at spaced locations on the surface of the glass pane;
first and second upstanding electrical lead attachment tabs secured in
electrical contact onto the first and second bus tabs;
an electrically resistive trace on the surface of the glass pane, formed of
electrically resistive material different from the electrically conductive
material of the bus pads, establishing an electrical interconnection
between the bus pads having a non-short circuit resistance value; and
security circuitry electrically connected to the detector assembly via the
upstanding electrical lead attachment tabs, for sensing and responding to
a change greater than a predetermined amount in the resistance value of
the resistive trace.
6. The motor vehicle glazing unit security system in accordance with claim
5 further comprising multiple additional glazing units mounted in the
motor vehicle, each having a tempered glass pane having a surface and a
glazing pane breakage detector assembly comprising:
first and second electrically conductive bus pads formed of electrically
conductive material on the surface of the glazing pane, and
an electrically resistive trace on the surface of the glazing pane, formed
of electrically resistive material different from the electrically
conductive material of the bus pads, establishing a non-short circuit
electrical interconnection between the bus pads,
and wherein the security circuitry electrically interconnects the detector
assemblies in series, for sensing and responding to a change greater than
a predetermined value in a cumulative resistance value of the resistive
traces.
7. The motor vehicle glazing unit security system in accordance with claim
6 wherein the cumulative resistance value is between 10 and 1,500 ohms and
the predetermined amount is between 5 and 50 ohms.
8. A motor vehicle glazing unit security system comprising:
a glazing unit mounted in a motor vehicle and comprising a tempered glass
pane having a surface;
a glazing pane breakage detector assembling comprising:
first and second electrically conductive bus pads of electrically
conductive material at spaced locations on the surface of the glass pane;
and
an electrically resistive trace on the surface of the glass pane, formed of
electrically resistive material different from the electrically conductive
material of the bus pads, establishing an electrical interconnection
between the bus pads having a non-short circuit resistance value;
security circuitry electrically connected to the detector assembly for
sensing and responding to a change greater than a predetermined amount in
the resistance value of the resistive trace; and
multiple additional glazing units mounted in the motor vehicle, each having
a tempered glass pane having a surface and a glazing pane breakage
detector assembly comprising:
first and second electrically conductive bus pads formed of electrically
conductive material on the surface of the glazing pane, and
an electrically resistive trace on the surface of the glazing pane, formed
of electrically resistive material different from the electrically
conductive material of the bus pads, establishing a non-short circuit
electrical interconnection between the bus pads;
wherein the security circuitry electrically interconnects the detector
assemblies in series, for sensing and responding to a change greater than
a predetermined value between 5 and 50 ohms in a cumulative resistance
value of the resistive traces between 10 and 1,500 ohms, and the resistive
traces have dissimilar configurations.
9. A motor vehicle glazing unit security system comprising:
a backlite mounted in a motor vehicle and comprising a tempered glass pane
having a surface;
a backlite breakage detector assembly comprising:
first and second electrically conductive bus pads of electrically
conductive silver-filled paint material on the surface of the glass pane
at a predetermined distance between 0.5 and 2.0 inches from each other,
first and second upstanding electrical lead attachment tabs secured in
electrical contact onto the first and second bus pads, respectively, and
an electrically resistive trace on the surface of the glass pane, formed of
electrically resistive polymeric material self-adhered to the surface of
the glass pane and different from the silver-filled paint material of the
bus pads, establishing an electrical interconnection between the bus pads
with an electrical resistance value between 500 and 1,500 ohms; and
security circuitry electrically connected to the detector assembly via an
electrical lead attached to the attachment tabs for sensing and responding
to a change in the resistance value greater than a predetermined amount
between 5 and 50 ohms.
Description
FIELD OF THE INVENTION
The present invention is directed to a window or other glazing unit wherein
a tempered glass pane or other frangible glazing pane carries a glazing
pane breakage detector assembly. The present invention is directed also to
a security system incorporating such glazing units.
BACKGROUND
Security systems are known for detecting breakage of a tempered glass pane
or other frangible glazing pane, for example, for detecting breakage of a
backlite in a motor vehicle. Such systems typically include means for
detecting breakage of the pane and means for responding to such breakage,
for example, by sounding an alarm or disabling the motor vehicle
powertrain. Glazing unit security systems have employed circuitry for
detecting loss of electrical continuity upon breakage of the glazing pane.
In U.S. Pat. No. 3,609,739 to Walter, a glazing security system employs an
electrically conductive strip forming a closed loop around the outer
perimeter of a glass pane. Such full perimeter strips, however, present
appearance problems, especially for motor vehicle windows. In addition,
known systems employing electrical continuity loss detection circuitry may
in some applications be defeated by a jumper cable attached between the
positive and negative terminals.
In commonly assigned U.S. Pat. No. 5,389,911 to Madau, an alarm system for
detecting glass breakage is disclosed, having security system circuitry
which, in addition to detecting complete loss of electrical continuity,
also can detect and respond to a change in electrical resistance values.
The electrical resistance values are determined by the electrical
resistance of a trace or patch of electrically resistive material carded
on a surface of the glazing pane. Multiple patches carded, one each, on
the windows of a motor vehicle are connected in series in the security
system of the Madau patent. A patch resistance value from 13-50 ohms is
suggested, with the patch material being deposited onto the surface of the
glass by silkscreening.
Suitable resistive materials are known for forming a suitable resistive
patch or trace on the surface of a glazing pane. Such materials can
present difficulties, however, in establishing secure electrical
connections to electrical leads from the security system circuitry. Such
difficulties can be especially significant in the context of high volume
production, such as a motor vehicle assembly line, where it is desirable
to form such structurally reliable electrical connection quickly, and with
good repeatability and repairability. It is an object of the present
invention to provide a glazing unit security system which is not easily
defeated by short-circuiting electrical terminals of the system, and yet
is readily adaptable to modem commercial assembly operations. These and
additional objects and advantages of the invention will be apparent from
the following general disclosure and detailed description of certain
preferred embodiments.
SUMMARY
In accordance with a first aspect, a glazing unit has a frangible glazing
pane, such as a tempered glass pane, carrying a glazing pane breakage
detector assembly on its surface. The detector assembly includes first and
second electrically conductive bus pads formed of electrically conductive
material on the surface of the glazing pane. The electrically conductive
material of the bus pads preferably is highly electrically conductive, and
forms a structurally secure attachment to the glazing pane surface. An
electrically resistive trace on the glazing pane surface is formed of
electrically resistive material different from the electrically conductive
material of the bus pads. The electrically resistive trace establishes
electrical interconnection between the bus pads. Electrical leads for
connecting the detector assembly to suitable security system circuitry can
be reliably and securely attached to the bus pads. Preferably, upstanding
attachment tabs are secured to the bus pads, for example, by electrically
conductive epoxy, solder or the like. Electrical leads can then be
connected to the upstanding attachment tabs, optionally being removably
attached. In preferred embodiments discussed further below, the resistive
trace is formed of polymeric material self-adhered to the surface of the
glazing pane. The resistive trace can be formed of materials which yield a
surface bond to the glazing pane which is not sufficiently structurally
sound to afford reliable attachment for an electrical lead connecting the
trace to security system circuitry, since that function is provided
instead by the highly electrically conductive bus pads.
In accordance with another aspect, a motor vehicle security system includes
a glazing unit as described above, mounted in a motor vehicle, for
example, as a motor vehicle backlite. Security system circuitry also is
mounted in the vehicle, electrically connected to the detector assembly of
the glazing unit, for sensing and responding to a change in the resistance
value of the resistive trace which exceeds a predetermined amount.
Those who are skilled in the art, that is, those who are skilled in this
area of technology, will recognize that the present invention provides a
significant technological advance having important commercial advantages.
The bus pads are easily and reliably formed, optionally using
silkscreening or other known techniques whose application to the present
invention will be readily apparent in view of this disclosure.
Silver-filled paint, currently used in forming heater grids or the like
for motor vehicle windows, can be used in such techniques to form highly
electrically conductive bus pads having structurally secure attachment to
a tempered glass or other glazing pane. With the benefit of the present
disclosure, it also will be apparent that commercially available
attachment tabs for attachment of electrical leads can be secured to the
bus pads using known materials and techniques, such as electrically
conductive epoxy, solder and the like. Thus, attachment tabs can be
provided with structurally sound attachment and good electrical connection
to the bus pads. In view of the present disclosure, it will be apparent
that such attachment tabs can provide significant cost, complexity and
reliability advantages in connecting electrical leads from security system
circuitry in the course of high volume commercial assembly operations. The
resistive trace interconnecting the bus pads can be readily formed using
known techniques and materials whose application to the present invention
will be readily apparent from the present disclosure. Resistive materials
can be selected which provide a fragile resistive trace on the surface of
the glazing pane, since the trace need not be relied upon in the present
invention to provide a structurally sound attachment for electrical leads
from security system circuitry. A fragile resistive trace is desirable and
advantageous for providing ready loss of electrical continuity in the
event of fracture of the glazing pane underlying the resistive trace. It
is not a disadvantage as in prior known systems, since attachment of
electrical leads from the security system circuitry need not rely on the
structural soundness of the resistive trace for a secure electrical
connection. Rather, such structurally secure attachment is provided by the
bus pads, as mentioned above.
It is a further significant advantage of the present invention that the
resistive value of the trace can be either predetermined or variable. The
resistive value can be predetermined by controlling the distance between
the bus pads and the configuration of the resistive trace interconnecting
them. The resistive value can be varied from one glazing pane to the next,
even given uniform spacing between the bus pads, by modifying the material
and/or the configuration (that is, the size, shape, etc.) of the resistive
trace. In accordance with one alternative embodiment, the resistive trace
can be painted onto a glazing pane by hand with deliberate variation in
its configuration. Security system circuitry can be readily provided by
those skilled in the art, which can use an initial reading of the
resistive value of the trace as a reference value against which future
readings are compared to detect any unacceptably large change in value.
Suitable circuitry can be provided, for example, in accordance with the
teachings of the above mentioned commonly owned U.S. Pat. No. 5,389,911 to
Madan, the entire disclosure of which is incorporated herein by reference.
Thus, the glazing units and security systems incorporating them, which are
disclosed here, can provide security against undetected breakage of the
glazing pane. Total loss of electrical continuity between the bus pads can
be detected by security system circuitry. Additionally, any attempt to
provide an auxiliary short circuit between the bus pads, for example, by a
jumper cable or the like between the attachment tabs, would provide an
altered resistive value which also can be detected by security system
circuitry. Especially in those embodiments wherein the resistive value of
the trace is variable from one glazing unit to the next, measuring the
resistive value of the resistive trace on one glazing unit would not
provide information useful for defeating a security system incorporating a
different one of such glazing units.
These and additional features and advantages will be further understood
from the following detailed description of certain preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
Certain preferred embodiments of the glazing unit disclosed here are
described below, including embodiments incorporating such glazing units in
a motor vehicle security system, with reference to the appended drawings
wherein:
FIG. 1 is a schematic perspective view of a glazing unit incorporating a
glazing pane, partially broken away, and a breakage detector assembly in
accordance with one preferred embodiment;
FIG. 2 is a section view of the glazing unit of FIG. 1, taken through line
2--2 of FIG. 1;
FIG. 3 is a section view of the glazing unit of FIGS. 1 and 2, taken
through line 3--3 of FIG. 1;
FIG. 4 is a schematic perspective view of a motor vehicle incorporating a
glazing unit security system in accordance with a preferred embodiment of
the invention; and
FIG. 5 is a schematic perspective view of the glazing unit of FIG. 1
showing a resistive trace with a non-straight line irregular path.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
It should be understood that glazing units in accordance with the present
invention and, in particular, the glazing pane breakage detector
assemblies of such glazing units, may have dimensions and configurations
differing from those of the preferred embodiments illustrated in the
appended drawings. The relative size and configuration of the bus pads,
resistive trace, electrical lead attachment tabs, etc., would be
determined in large part by the particular application for which the
glazing unit is intended. It will be well within the ability of those
skilled in the art, given the benefit of the above disclosure and the
following detailed description of certain preferred embodiments, to select
suitable component configurations, materials, production techniques and
the like, to meet the needs of such particular applications. It also
should be understood that the dimensions of certain features or aspects
shown in the appended drawings have been enlarged or otherwise modified
for clarity of illustration. Thus, for example, the thickness of the bus
pads and resistive trace in the embodiment of FIGS. 1-3, relative the
thickness of the underlying glazing pane, are greater than would likely be
used in a routine application of the invention in a motor vehicle security
system.
While the glazing units disclosed here, and security systems incorporating
them, can be employed in diverse applications, they are especially
advantageous for use in motor vehicle applications. Accordingly, the
following detailed description of certain preferred embodiments focusses
primarily on motor vehicle security system applications. In particular,
the present invention is advantageous for use in side windows and
especially backlites formed of tempered glass. Tempered glass undergoes
overall shattering upon sustaining any significant fracture anywhere in
the expanse of the glass. Thus, any significant fracture of one of these
glazing panes will cause fracturing also of that portion of the pane under
the resistive trace. The resistive trace is sufficiently fragile that such
fracturing of the underlying pane will cause loss of electrical continuity
of the trace. The resulting loss of electrical continuity can be detected
by associated security system circuitry.
Thus, the resistive trace can be formed of any suitable material which is
sufficiently robust to withstand handling during assembly and the use
environment of the intended application, and yet sufficiently fragile that
breakage of the glazing pane results in loss of its electrical continuity.
The resistive trace can be formed of various different materials and by
various techniques, so as to be sufficiently fragile as to have
insufficient structural integrity to maintain electrical continuity upon
shattering of the underlying glazing pane. Suitable materials for forming
the resistive trace are commercially available and will be apparent to
those skilled in the art in view of this disclosure. Suitable film-forming
conductive inks are available, including, for example, product No. 114-11
from Creative Materials, Inc. (Tyngsboro, Mass.), either alone or in
mixture with their product No. 114-34. Another example is ORMET 2005
conductive ink from Toranaga Technologies, Inc. Conductive epoxies and
other curable polymeric materials also are commercially available and
suitable for certain preferred embodiments. One particularly preferred
resistive material is product No. 115-50, silver-filled electrically
conductive ink, available from Creative Materials, Inc. Various conductive
epoxies are known to those skilled in the art, and the curing procedure
will depend upon the conductive epoxy selected. Certain conductive
epoxies, for example, are self-curing at ambient conditions, or by
exposure to ultraviolet or other actinic radiation, by thermal curing upon
exposure to elevated temperatures, or the like. Suitable conductive epoxy
material is disclosed, for example, in U.S. Pat. No. 5,114,756 to
Mirabeau. Alternative suitable conductive epoxies are commercially
available and will be apparent to those skilled in the art in view of this
disclosure.
These liquid and semi-liquid film-forming materials can be applied, for
example, by a roller directly onto the surface of the glazing pane.
Silkscreening and like application processes also are typically suitable
for such materials. In addition, as mentioned above, it may be desirable
in certain applications to apply the resistive trace in a random manner,
for example, by painting the trace onto the glazing pane freehand in a
non-straight, irregular pattern or path between the bus pads. A resistive
material having certain electrical conductivity properties will in this
fashion yield a different resistive value for the detector assembly from
one glazing pane to the next. Using security system circuitry adapted to
employ an initial resistance reading as a reference value, would in this
case result in a unique and unpredictable resistance value for each
glazing unit. It would, therefore, be quite difficult to defeat the
security system by attaching a jumper cable between the two bus pads as a
substitute for the resistive trace (whose electrical conductivity would,
presumably, be thereafter lost due to intentional breaking of the glazing
pane), since it would be difficult to predict the exact required resistive
value for such a jumper cable. It will be within the ability of those
skilled in the art to provide such security system circuitry, given the
benefit of the present disclosure, including the incorporated disclosure
of the above mentioned Madau patent.
While the resistance value will vary from one application to another, an
exemplary range for motor vehicle security system applications is from 10
ohms to 1,500 ohms, measured from one bus pad to the other. A value of 500
ohms to 1,200 ohms is suitable, for example, since higher resistance
values result in a smaller drain on the motor vehicle battery. The
security system circuitry would detect and respond either to a loss of
electrical continuity between the bus pads, presumably corresponding to
breakage of the glazing pane, and/or to a change of electrical resistance
between the bus pads exceeding a predetermined amount. Such predetermined
amount of resistance change will depend, of course, on the particular
application and on the overall resistance value. In that regard, it should
be recognized that the resistance value seen by the security system
circuitry may be a cumulative value resulting from the series connection
of multiple resistive traces, such as one on each of several windows of
the motor vehicle. For a resistance value between 500 and 1,200 ohms (for
an individual resistive trace or multiple traces connected in series), for
example, the amount of change tolerated by the security system circuitry
before responding can be preset at a value of about 5 to 50 ohms.
The security system can respond to a loss of electrical continuity or
unacceptably large change in resistivity by an audible and/or visible
alarm. The security system may also be adapted to disable normal operation
of the motor vehicle. In preferred motor vehicle applications, the
security system circuitry determines the electrical continuity and
resistance value of the breakage detector assemblies, either directly or
indirectly, continuously or, more preferably, repeatedly. The frequency at
which the security system tests the breakage detectors can vary widely,
depending upon the available power resources, level of security desired,
and other aspects of the particular application. The frequency (or average
frequency) can be set, for example, between once every few seconds and
once every hundred milliseconds. It will, in general, be within the
ability of those skilled in the art to select a suitable test frequency,
given the benefit of the present disclosure.
It is especially important for motor vehicle applications that the detector
assembly not have significant adverse impact on the appearance of the
vehicle. For this reason, the detector assembly preferably is located
along a peripheral edge of the glazing pane, most preferably on an inside
surface hidden behind black-out paint or the like. In any event, the
detector assembly most preferably is kept to a small overall size. For
this reason, the bus pads should be as closely spaced as possible,
consistent with the need to lose electrical continuity upon fracture of
the glazing pane. Motor vehicle backlites and side window glass typically
employ tempered glass panes which undergo overall fracture into pieces of
one-half inch size or smaller. Thus, in particularly preferred embodiments
the bus pads are carded on a tempered glass pane, spaced from each other
one-half inch to three-quarter inch apart.
A glazing unit in accordance with one preferred embodiment is illustrated
in FIGS. 1 to 3, comprising a tempered glass pane 10 having surface 12
carrying a glazing pane breakage detector assembly 14. The detector
assembly includes a first highly electrically conductive bus pad 16 and a
second such bus pad 18 at a predetermined distance from the first bus pad
16. The distance between the bus pads is the shortest distance between
them, that is, the distance between edge 20 of bus pad 16 and edge 22 of
bus pad 18. Bus pads 16 and 18 preferably are silkscreened onto surface 12
of glass pane 10 using silver-filled paint, such as is currently in use to
make bus bars for backlite heater grids and the like. Attachment tabs are
secured to the bus pads with good electrical contact. Specifically, a
first attachment tab 24 is attached to upper surface 17 of first bus pad
16, for example by conductive epoxy, soldering, etc. While electrical
leads from the security system circuitry can be soldered or otherwise
attached directly to the bus pad, use of attachment tabs is preferred and
advantageous. Significant advantage is obtained, for example, in
facilitating attachment of the electrical leads in a commercial motor
vehicle assembly line operation. Exemplary attachment tabs include, for
example, URX tabs which provide an upstanding attachment flange having a
bent-over end. An upstanding attachment tab is schematically illustrated
by upstanding flange 26 of attachment tab 24. Other suitable, commercially
available attachment tabs include, for example, Molex tabs which provide a
female receptacle for receiving electrical leads. Additional suitable
attachment tabs are commercially available, and their application in the
present invention will be apparent to those skilled in the art, given the
benefit of the present disclosure. A second attachment tab 28 having
upstanding attachment flange 30 is secured with good electrical contact
onto upper surface 19 of the second bus pad 18. In FIG. 3 an electrical
lead 32 is shown attached to upstanding flange 26 of attachment tab 24.
Specifically, spring clip 34 of electrical lead 32 is shown to be received
over upstanding flange 26. As thus far described, the detector assembly
components have structurally sound attachment to glazing pane 10, with
good electrical connection between the bus pads and the attachment tabs.
The detector assembly 14 of the glazing unit illustrated in FIGS. 1-3
further comprises a resistive trace 36 bridging the gap between the bus
pads 16, 18. The resistive trace is seen to be straight, but could instead
follow an irregular path, resulting in a resistance value different from
that which would be obtained with a straight trace between the bus pads
(as seen in FIG. 5). The resistive trace overlaps the bus pads somewhat to
establish good electrical connection. The resistive trace 36 can be
applied, for example, by silkscreen, roller, hand-held paintbrush, etc.,
after the bus pads have first been formed on the glass pane. Resistive
trace 36 is advantageously fragile, so as to undergo loss of electrical
continuity in the event of the fracture of the underlying glass pane. The
fragility of the conductive trace is no disadvantage regarding the
structural integrity of the detector assembly, since the attachment tabs
24, 28 are secured to the bus pads 16, 18, rather than to the resistive
trace. Preferably, the resistive trace is quite short to minimize its
aesthetic impact on the outward appearance of the motor vehicle glazing
pane to which it is attached. Most preferably, it is between 0.5 and 2.0
inches long. To facilitate accurate sizing of the resistive trace, the bus
pads can be applied having a predetermined distance between them equal to
the intended length of the resistive trace. The trace would overlap the
two bus pads and its effective length would be the distance between the
bus pads, that is, preferably, between 0.5 and 2.0 inches.
A motor vehicle glazing unit security system is illustrated in FIG. 4,
comprising multiple glazing units fitted with a detector assembly, as
described above. Motor vehicle 40 is seen to have a front driver door
window 42 of tempered glass, carrying a breakage detector 43 at its lower
left corner (as viewed in FIG. 4) in an area below the so-called beltline
44, such that it would not be visible during normal operation of the
window between its open position and its closed or full-up position.
Similarly, rear door window 46 carries at its forward lower corner a
breakage detector 47. Backlite 48 carries breakage detector 49 in a lower
corner. Breakage detectors 43, 47 and 49 are in series electrical
connection by means of electrical lead 50. Electrical lead 50 extends from
security system circuitry 52 to a first attachment tab of breakage
detector 43. A second portion of lead 50 extends from the second
attachment tab of breakage detector 43 to the first attachment tab of
breakage detector 47. A next portion of lead 50 extends from the second
attachment tab of breakage detector 47 to the first attachment tab of
breakage detector 49. The second attachment tab of breakage detector 49
can be grounded, or extend on to further series connections. A second lead
54 from security system circuitry 52 extends to series electrical
connection of breakage detectors attached to windows on the passenger side
of vehicle 40. The breakage detectors are seen to be advantageously small
to minimize any interference with the visual aesthetics of the vehicle.
Backlite 48 and side windows 42 and 46 are formed of tempered glass. A
fracture in any of these glass panes would result in an overall shattering
of that pane, and a consequent loss in electrical continuity of a
resistive trace bridging between the bus pads of the breakage detector
assembly carried by that pane. Such loss of electrical continuity would be
detected by circuitry 52 which has electrical power feed from a vehicle
battery or other power source. Circuitry 52 is adapted to respond upon
detecting such loss of continuity, for example, by actuating an audible
alarm, a visual alarm, and/or disabling means for preventing normal
operation of the vehicle. These and other alarms and disablement means are
commercially available, and their application in the present invention
will be readily apparent to those skilled in the art, given the benefit of
the present disclosure. Circuitry 52 is adapted further to respond to a
change in the resistance value of the series electrical circuits
interconnecting the breakage detector assemblies. An attempt to mask the
loss of electrical continuity of a detector assembly by applying a jumper
wire or cable between the two bus pads would yield a different cumulative
resistance value, and circuitry 52 would respond to change in value.
Another preferred embodiment is shown in FIG. 5. Resistive trace 37 in this
embodiment follows an irregular path between bus pads 16, 18, resulting in
a resistance value different from that which would be obtained from the
straight line path of resistive trace 36 of FIG. 1.
In view of the foregoing disclosure and discussion of various preferred
embodiments of the invention, those skilled in the art will readily
understand that suitable additions, modifications and alternative
embodiments are within the true scope and spirit of the invention. All
such modifications, additions and alternative embodiments are intended to
be included within the scope of the appended claims.
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